This invention relates to carburetors for internal combustion engines, and while not limited thereto, is directed particularly to carburetors employed on aircraft engines, and is an improvement over that disclosed and claimed in my prior Pat. No. 4,277,424, dated July 7, 1981.
One of the known and primary causes of aircraft engine failure is carburetor icing. My investigation into this problem leads me to believe that little real, sound information is available on carburetor icing, particularly with regard to the places in the carburetor where ice forms and the effect thereof on the operation of the engine, and interference with fuel metering.
My investigations have revealed that the primary cause of engine failure or partial failure due to carburetor ice comes about because ice builds up on the engine side (downstream side) of the throttle valve.
Most aircraft carburetors are provided with both idling systems and main jet systems to supply the fuel to the air stream flowing through the carburetor body. In aircraft carburetors (and, so far as I am aware, most automobile carburetors) it is customary for the idle jet system to be in communication with the main jet system, although such is not always the case.
Recognition of carburetor icing is generally limited to the build-up of ice which occurs around the upstream outer rim of the throttle valve, between the outer rim of the throttle valve and the carburetor wall, closing or restricting the air passage and causing engine stall under certain atmospheric conditions.
In addition to this type icing I have discovered that ice commences to form on the engine side of the throttle valve on the side or quadrant adjacent the idle jet. Thus, with the throttle valve in partially closed position the ice may cover substantially one-half of the throttle valve; continued build-up of ice may occur on the downstream side of the throttle valve adjacent the idle jet even when the throttle valve is in the substantially full open position. Thus, substantially the entire surface of the throttle valve becomes covered with ice, which ice cake extends to the side walls of the carburetor body, adjacent the idle jet. In either partial or full open position of the throttle valve there is a restriction of flow of air through the carburetor body adjacent the idle jet, resulting in a tremendous reduction in pressure at the mouth of the idle jet and in the idle jet system. Since this system is in communication with the main jet system, under either of these conditions I have discovered that instead of fuel being inspirated from the main jet, there is fuel starvation of that jet simply because there is greater negative pressure at the fuel supply end of the main jet than at the fuel discharge thereof. Under these circumstances the main jet is starved of fuel. Since the effective diameter of the idle jet is less than that of the main jet the idle jet is too small to supply the requisite quantity for full engine operation. Furthermore, with partial build-up of ice on the throttle valve and at partial opening of the throttle valve, there can be a condition resulting in mixture so rich as to cause engine failure or at the least rough operation and a waste of fuel. Continued operation under the latter conditions, namely without changing the throttle setting, can result in engine failure due to an over-rich or lean mixture (limited generally to a rich mixture in systems where the idle passage and main passage are not in communication).